Hey, slightly late to the party, but I had a similar issue and manage to "fix" it (details later). It's not EXACTLY the same issue, so I don't know if this would work for the OP or not, but others finding this thread may find this solution useful.
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In my case, I also had no problem creating the bootable usb (via rufus), booting it, and installing, though I installed to a different drive than my windows (7) installation. I had already prepared an empty partition ahead of time via Windows 7's partition manager, so during the nobara installation I used the "replace partition" (or some phrasing like that) option and selected the empty partition. Note that I did change the boot from its default value of sda (which is my windows 7 drive) to sdb (which is the drive I was installing nobara to). Unsure if that's important.
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Once installation was completed and I restarted, it booted into windows 7 with no grub or other boot menu before-hand. I found
this post on the official nobara site, but following the instructions there did not solve the issue for me. I rebooted and used the motherboard boot selector to manually select the drive with nobara. This worked, but grub only showed nobara and did not have an option for windows 7. After some reading, I realized that nobara is EFI and my windows 7 install is not, which seems to be why nobara grub isn't adding an option for it.
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Now for something a little extra tricky; according to my default boot order, nobara should have booted before windows 7 anyway, so why didn't it? Well, that's because my motherboard settings have two options for boot management - "UEFI" and "LEGACY + UEFI". Obviously if I choose "UEFI" windows 7 is inaccessible, so it's the hybrid option...but what's really tricky is that it seems to have a bug where once it attempts any non-EFI boot device, future EFI boot devices fail (or at least my nobara install did). I had to make sure it attempted booting nobara before all non-EFI boot options (I had a non-EFI usb boot option before it previously.
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Once I changed the default boot order, I now automatically got the nobara grub on startup instead of going straight into windows 7. Here's where it's a "fix" and not a fix. Windows 7 isn't accessible from there. I still have to manually select whichever OS is not the default straight from the motherboard boot menu if I want to access it.
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Not perfect, but I can deal with it. I'll just set my default boot order according to which OS I'm currently using the most, and access the other via the MB boot menu. Hopefully this helps someone else.